Miniaturization and sophistication of magnetic devices are followed by demand for magnetic thin film materials having high saturation magnetization and high permeability in the high frequency of GHz range.
For example, the monolithic microwave integrated circuit (MMIC), for which demand is growing mainly for use in wireless transmitters/receivers and portable information devices, is a high frequency integrated circuit having a configuration in which active elements such as transistors and passive elements such as transmission line, resistors, capacitors and inductors are integrated on a semiconductor substrate made of Si, GaAs, InP and the like.
In such an MMIC, the passive elements, in particular, the inductors and capacitors occupy larger areas than the active elements. The occupation of larger areas by the passive elements as a result leads to mass consumption of expensive semiconductor substrates, namely, the cost rise of the MMIC. Accordingly, now it is a challenge to reduce the areas occupied by the passive elements for the purpose of reducing the chip area and thereby lowering the manufacturing cost of the MMIC.
As the inductors used in MMICs, planar spiral coils are frequently used. In this connection, there has already been proposed a method (in other words, a method for obtaining an inductance comparable with a conventional inductance even by using a small occupied area) for increasing the inductance of such a spiral coil by inserting a soft magnetic thin film on the top and back sides or on one side of the spiral coil (for example, J. Appl. Phys., 85, 7919 (1999)).
However, for the purpose of applying a magnetic material to the inductor in an MMIC, it is demanded that firstly, a thin film magnetic material, which is high in permeability and low in loss in the high frequency of GHz range, should be developed. Additionally, high resistivity is also demanded for the purpose of reducing the eddy current loss.
So far, alloys comprising as the main component Fe or FeCo have been well known as materials having high saturation magnetization. However, when a magnetic thin film made of an Fe-based alloy or an FeCo-based alloy is prepared by means of a deposition technique such as the sputtering technique, the saturation magnetization of the film obtained is high, but the coercivity thereof is high and the resistivity thereof is low, so that satisfactory high frequency properties thereof can be hardly obtained.
On the other hand, Co-based amorphous alloys are known as materials excellent in soft magnetic properties. Such a Co-based amorphous alloy mainly comprises an amorphous substance comprising Co as the main component and one or more elements selected from the group consisting of Y, Ti, Zr, Hf, Nb, Ta and the like. However, when a Co-based amorphous alloy having zero magnetostriction composition is formed by means of a deposition technique such as the sputtering technique, the permeability of the film obtained is high, but the saturation magnetization thereof is of the order of 11 kG (1.1 T), and lower than those of Fe-based alloys. Additionally, for the frequencies higher than 100 MHz, the loss component (the imaginary part of the permeability, μ″) becomes large and the quality factor Q comes to be 1 or less, so that the film concerned cannot be judged to be suitable as a magnetic material to be used in the high frequency of GHz region.
For the purpose of actualizing the inductor for use in the GHz region by use of such hardly applicable materials, an attempt has been made to shift the resonance frequency to the higher frequencies by micro-patterning a magnetic thin film so as to be increased in shape magnetic anisotropy energy (for example, J. Magnetics Soc. Japan, 24, 879 (2000)). However, this method involves a problem such that the production process tends to be complicated and additionally the effective permeability of the magnetic thin film is lowered.
Under such actual circumstances as described above, various proposals have hitherto been made for the purpose of improving the high frequency properties of the soft magnetic thin film. The fundamental guidelines for the improvement include the suppression of the eddy current loss and the increase of the resonance frequency. Specific measures for suppressing the eddy current loss which have been proposed include a multilayered configuration formation by alternately laminating a magnetic layer and an insulating layer (a high electric resistance layer) (for example, Japanese Patent Laid-Open No. 7-249516) and a granularization of metals and nonmetals (oxides, fluorides) (for example, J. Appl. Phys., 79, 5130 (1996)). However, the multilayer film methods involve the insertion of the high electric resistance nonmagnetic phase and hence lead to a problem such that the saturation magnetization is lowered. In the case of the metal-nonmetal granular film, a permeability is 200 or less, leading to a problem that the permeability is low.
On the other hand, high saturation magnetization thin films each made of a multilayer film formed by alternately laminating a soft magnetic layer and a high saturation magnetization layer has been investigated. More specifically, there have been reported various combinations such as CoZr/Fe (J. Magnetics Soc. Japan, 16, 285 (1992)), FeBN/FeN (Japanese Patent Laid-Open No. 5-101930), FeCrB/Fe (J. Appl. Phys., 67, 5131 (1990)), and Fe—Hf—C/Fe (J. Magnetics Soc. Japan, 15, 403 (1991)). Any one of these combinations has an effect of enhancing the saturation magnetization. However, any one of these combinations cannot yield high permeability in the high frequency region, no application to the GHz frequency region being able to be expected.
Under such actual circumstances as described above, the present invention has been invented and takes as its object the provision of a high frequency magnetic thin film having high permeability and high saturation magnetization in the high frequency of GHz region. Additionally, the present invention takes as its another object the provision of a magnetic device using such a magnetic thin film.